Sirisena, in his ceremonial speech during the inaguration of the 225-member assembly, pledged to introduce consensual politics with the new government.
He asked the newly-elected lawmakers to draft political and economic reforms to promote ethnic reconciliation in the post-war era.
"It will be the duty of this new parliament to decide on the system of executive presidency," Sirisena said adding that the 20th amendment to the Constitution incorporating electoral reforms would be presented soon.
Both the major political parties in Sri Lanka -- the United National Party (UNP) and the Sri Lanka Freedom Party (SLFP) -- are partners in the new government.
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The two major parties have ruled this country for 67 years now, and it is time to end rivalries and forge unity, Sirisena said.
Sirisena said he would invite Sri Lankan intelligentsia, who now reside overseas, to return to the country to taste the new culture of "consensual politics."
Sirisena said the government would follow a foreign policy that is Asia-centric.
My government has been able to change the adverse international opinion on the country in the past seven months, Sirisena said.
The government would ensure development through communal harmony and reconciliation, he said.
Sirisena's SLFP and Wickremesinghe's UNP are to join the new government, as the UNP failed to win absolute majority in the general election.
The assembly had met today to elect new parliamentary officials. Senior politician Karu Jayasuriya was unanimously elected Speaker of the assembly.